🚀 go-pugleaf

In article <3559@idunno.Princeton.EDU>, lseltzer@phoenix.Princeton.EDU (Linda Ann Seltzer) writes:
> I'm not familiar with wht is available for people who have some
> hearing, but my understanding is that there is some DSP work going
> on in relation to cochlear implants.  In cochlear implants, the
> nerve is stimulated directly, bypassing the non-functioning
> cochlea.  For persons who do not have nerve damage or malfunction,
> the signals can be perceived and understood, even though they do
> not sound like real speech.  Patients can be trained to recognize
> speech in these signals.  DSP work is the goal of improving the
> signals which are transmitted to the patient, so that they produce
> perceived sounds which correspond more closely to speech and which
> are easier to interpret.

A good description of the process, which is what we do research on in
this lab. The electrodes are implanted *in* the cochlea and stimulate
the auditory nerve at different points. Since for some deaf people
there is damage to the hair cells, which translate motion of fluids
in the cochlea to nervous impulses, these devices essentially replace
the hair cells and middle ear with electrodes and a microphone.
There are two multi-channel approaches being used: the Ineraid,
which has 8 electrodes and uses the output from 4 bandpass filters to
stimulate a pre-selected 4 electrodes, and the Nucleus, which has 22
electrodes and stimulates different electrodes depending on the primary
frequencies in the sound. 

The Nucleus may indeed have some digital processing, but I have heard that
the builders are in the process of re-examining their stimulation scheme. If
I am not mistaken, they would like to pre-select some of the channels to
always carry signal, somewhat like the Ineraid. The Ineraid has *no* digital
processing. (Why do DSP for a low-power compact gain control, filters, and
V/I conversion? It would be like using a tennis racket to play ping-pong.)

We are examining a high-speed switching scheme for the Ineraid: stimulating
the electrodes sequentially with impulses from the output of their respective
filters, but I would hardly call that DSP. It's still analog signals, just
multiplexed in the time domain. (We expect it to reduce cross-talk.)
There was a fairly good article on this stuff in a recent issue of Scientific
American. If you're curious about it, you can look it up there.

The nice thing about the scheme is that it takes advantage of the way
the auditory nerve is already set up to take spatial locations as a spectral
analysis and signal amplitude and timing information as direct information.
I've had a number of arguments on why a similar process is not possible for
synthetic sight. The eye has too much data processing, in my opinion,
occurring before the optic nerve to pull the same sort of thing. Also,
the cochlea where our electrodes is a very stable bony structure: the
eye is *not*, and a fine electrode array all over the back of someone's
eye does not seem reasonable.

Disclaimer: I am the electrical engineer for the lab, not a clinician
or audiologist. Any questions on the use or appropriateness of these
devices for someone to use should be addressed to a medical expert.

-- 
			Nico Garcia
			Designs by Geniuses for use by Idiots
			eplunix!cirl!raoul@eddie.mit.edu